In knitted products such as shoe uppers, knitwears for sports or body correction, and knitted products for industrial materials, a common basic design is developed for designs of various sizes. If knitted products of different sizes are similar to each other, data of a knitted product for one size may be reduced or expanded to obtain data for other sizes. However, the knitted products of separate sizes are often not similar to each other, and thus it is necessary to repeatedly test knit knitted products for each size. For example, the group of shoe uppers have 13 sizes from 24 cm to 30 cm with an interval of 0.5 cm. It is a labor-consuming job to repeatedly test knit shoe uppers of 13 sizes in order to get the knitting data for satisfactory shoe uppers.
Patent Literature 1 (JP2015-175082A) proposes the simulation on the knitting data of sizes of knitted fabrics in order to obtain the knitted fabrics of satisfactory sizes, without performing the test knitting. Further, if the errors in the sizes of the knitted fabrics may be simulated, the pattern data representing the designs of the knitted fabrics or the like may be corrected, and the knitted fabrics of the desired sizes may be knitted. However, in particular, in the case of shoe uppers, highly accurate knitted sizes are required, and it is difficult to simulate the exact knitted sizes after knitting in consideration with the influences of physical properties of knitting yarns and the mechanisms of the knitting machine, and the like. Accordingly, it has not been practical to acquire knitting data for the desired sizes without performing the test knitting. The same applies to other knitted products which need highly accurate knitted sizes.